P.C.C. is Plain Cement Concrete - this is used for providing a firm and level base to any foundation, flooring or under any other load bearing component of a structure.
R.C.C. is Reinforced Cement Concrete and comprises of cement concrete in a specific ratio for the strength to be achieved for the job, however, since it contains mild steel bars, it is called R.C.C. The purpose of steel bars is to lend tensile strength to a roof slab, projections and so on.
D.P.C. is a Damp Proof Course - It is a layer of cement concrete laid at ground floor level only
[sometimes it is reinforced too] and as the name suggests its main use is to prevent moisture to rise in the structure from the foundations / soil around structures.